"We welcome measures that protect the rights and safety of consumers and the overall integrity of e-commerce channels and will continue to work closely with our partners through this process," a2 Milk said in a notice to the NZX.
Oyvinn Rimer, senior research analyst at Harbour Asset Management, said the announcement builds on last year's commerce law and kicks off with a multi-agency research programme to identify illegal activities on e-commerce platforms.
"No specific details but there is broad based e-commerce scope - with no reference to single products like infant milk," he said in a note.
China's announcement contained "very tough" language about the severe penalties involved, he said.
"Personally, it reads well for a2 Milk being a compliant and registered brand with legitimate distribution," Rimer in a note.
Shares in a2 Milk were trading down 34c or 2.4 per cent at $13.96 in late afternoon trade.
One fund manager said it appeared that a2 Milk had been caught up with the trend on the ASX - where a2 Milk is also listed - of profit-taking among the so called "growth" stocks.
He said weakness in the share price did not appear to be connected to the announcement
Harbour Asset has a stake in a2 Milk.